Docking protein Gab2 is phosphorylated by ZAP-70 and negatively regulates T cell receptor signaling by recruitment of inhibitory molecules.
To maintain various T cell responses and immune equilibrium, activation signals triggered by T cell antigen receptor (TCR) must be regulated by inhibitory signals. Gab2, an adaptor protein of the insulin receptor substrate-1 family, has been shown to be involved in the downstream signaling from cytokine receptors. We investigated the functional role of Gab2 in TCR-mediated signal transduction. Gab2 was phosphorylated by ZAP-70 and co-precipitated with phosphoproteins, such as ZAP-70, LAT, and CD3zeta, upon TCR stimulation. Overexpression of Gab2 in Jurkat cells or antigen-specific T cell hybridomas resulted in the inhibition of NF-AT activation, interleukin-2 production, and tyrosine phosphorylation. The structure-function relationship of Gab2 was analyzed by mutants of Gab2. The Gab2 mutants lacking SHP-2-binding sites mostly abrogated the inhibitory activity of Gab2, but its inhibitory function was restored by fusing to active SHP-2 as a chimeric protein. A mutant with defective phosphatidylinositol 3-kinase binding capacity also impaired the inhibitory activity, and the pleckstrin homology domain-deletion mutant revealed a crucial function of the pleckstrin homology domain for localization to the plasma membrane. These results suggest that Gab2 is a substrate of ZAP-70 and functions as a switch molecule toward inhibition of TCR signal transduction by mediating the recruitment of inhibitory molecules to the TCR signaling complex.
Pubmed ID: 11572860 RIS Download
Adaptor Proteins, Signal Transducing | Animals | Antigens, CD | Antigens, CD3 | Antigens, Differentiation, T-Lymphocyte | Binding Sites | Blotting, Western | Carrier Proteins | Cell Line | Cytokines | DNA | Dose-Response Relationship, Drug | Flow Cytometry | Humans | Hybridomas | Interleukin-2 | Intracellular Signaling Peptides and Proteins | Jurkat Cells | Lectins, C-Type | Luciferases | Lymphocyte Activation | Membrane Proteins | Mice | Mutation | Phosphatidylinositol 3-Kinases | Phosphoproteins | Phosphorylation | Precipitin Tests | Protein Binding | Protein Structure, Tertiary | Protein Tyrosine Phosphatase, Non-Receptor Type 11 | Protein Tyrosine Phosphatase, Non-Receptor Type 6 | Protein Tyrosine Phosphatases | Protein-Tyrosine Kinases | Receptors, Antigen, T-Cell | SH2 Domain-Containing Protein Tyrosine Phosphatases | Signal Transduction | Structure-Activity Relationship | Transfection | Tyrosine | ZAP-70 Protein-Tyrosine Kinase | src Homology Domains